Man's concern with the hazards associated with the ready combustibility of textiles has been continuous since the discovery and utilization of fire. Today it is desirable that certain fabrics such as curtains and drapes, decorative fabrics and sometimes upholstery and floor coverings in public buildings be flame resistant. It is highly desirable that certain clothing items such as children's pajamas be flame resistant. Many special purpose garments, such as welders' and steelworkers' overalls, fire fighters' clothing, and certain types of military clothing must be flame resistant.
Several factors generally affect flame resistance of a textile. First, the composition of the fibers must be considered. Natural fibers (such as cotton, flax, silk, wool), regenerated fibers (such as rayon), the man made fibers (such as nylons, vinyls, acrylics), and the inorganic fibers (such as glass and asbestos) have a varying combustility and flame resistance depending on their chemical make-up. Of course, the weight and construction pattern of the fabric makes a significant difference in ease of burning. Lightweight, loose weave fabrics usually burn much faster than heavier fabrics.
The terms used in connection with flame resistant fabrics are sometimes confusing. "Fire resistance" and "flame resistance" are very often used in the same context as the terms "fireproof" and "flameproof." A textile which is flame resistant or fire resistant will not continue to burn or glow once the source of ignition has been removed although there will be some change in the physical and chemical characteristics. Fireproof or flameproof, on the other hand, refers to a material which is so resistant to flames that no appreciable change in physical or chemical properties is noted. Glass is an example of a fireproof material; however, if flame is applied long enough, it will melt.
Fabrics comprising mineral fibers such as asbestos or glass fibers, while flameproof, have several drawbacks. They are uncomfortable when in contact with the skin; they are highly heat conductive; and usually they must be blended with other fibers such as cotton to provide adequate strength and flexibility to the fabric. When the cotton or other fabric becomes burned or charred, the asbestos or glass fabric becomes very brittle and may fall apart. Glass fibers begin to lose their strength around 350.degree.C and asbestos fibers dehydrate and become friable at about 550.degree.C. In intense heat they melt away. Wool and other animal fiber fabrics have a relatively high ignition temperature and burn slowly. Wool has a bulky ash which is very brittle and, therefore, burnt wool falls apart easily. Cotton and other cellulose type fabrics are extremely flammable without chemical treatment which is of limited value.
Most man made fabrics melt rapidly when in contact with flames or at temperatures somewhat above 150.degree.C. For example, polyethylene fabrics melt between 110.degree. and 120.degree.C; polyvinylidene chloride fabrics melt between 140.degree. and 150.degree.C; modacrylics (copolymers) melt at about 170.degree.C; polyesters (terephthalic acid derivatives) melt at around 250.degree.C; polyacrylonitrile (P.A.N.) fabrics soften at about 250.degree.C. The common polyamides melt at low temperatures, for example, nylon 6 melts at 210.degree.C and nylon 66 at 250.degree.C. It should be understood that synthetic fibers lose their strength at temperatures much below their melting points.
Of the synthetic fabrics, only special polyamides, polyacrylonitriles and fluorocarbons have generally been considered flame resistant. There are special polyamide fabrics that are more resistant to a flame than the common nylons but only retain their strengths to temperatures of about 225.degree.C and at about 325.degree.C decompose into a friable char. The polyacrylonitriles shrink at elevated temperatures and might under unusual conditions be the source of poisonous gases. The fluorocarbon fabrics (polytetrafluoroethylene) give off a poisonous vapor above 200.degree.C.
According to the teachings of this invention, there is provided a fabric having the following advantages: It is flame resistant. It does not melt. It has a low thermal conductivity. It is not uncomfortable when adjacent the skin as are mineral or woolen fabrics. The flexibility of the fabric is substantially equivalent to nylon. It chars producing carbon fibers with sufficient strength to maintain an integral protective cloth. It is chemically resistant and gives off no poisonous gases on heating.